Inachus or Inachos (Greek: Ίναχος) is:
- Inachos, a former municipality in Greece, Aetolia-Acarnania Regional Unit
- Inachos, a village in Greece, Argolis Regional Unit
- Inachos, a river flowing into the Aegean Sea
- Inachus, a king of Argos and personification of the same named river
- Inachos, a river flowing into the river Achelous
- Inachus, a genus of crabs